This invention relates to a process for plasma deposition and a plasma CVD apparatus, specifically a single substrate processing plasma CVD apparatus. The invention is applicable to, for instance, a plasma CVD process or the like for film formation to form an electronic material for a semiconductor device or the like.
In the prior art single substrate processing plasma CVD apparatus, chamber plasma cleaning is done once right after each deposition cycle. This is shown in FIG. 2. As shown, cleaning IIa is done right after a deposition cycle Ia, and cealing IIb is done again right after the next deposition cycle Ib.
This is done so because during the deposition CVD films are formed on the electrodes as well. If a deposition cycle is done right after the preceding cycle, i.e., without cleaning the chamber after the preceding cycle, the intensity of the electric field between applied between electrodes is reduced compared to the value in the preceding cycle, thus leading to non-unifrmity of the thickness of the CVD film and quality (etching rate, stress, etc.) thereof. For this reason, right after a deposition cycle the chamber is plasma cleaned once to remove CVD films formed on the electrodes. In the prior art, however, the time that is required for the cleaning sequence increases the total processing time and thus reduces the processing capacity of the apparatus.
It may be thought that if there is an adequate power meter which can reliably monitor the effective inter-electrode power, continuous deposition may be possible even in the prior art because it is possible to provide an adequate high frequency output at an adequate timing and thus make the electric field between the electrodes constant. Actually, however, the impedance including the electrodes, particularly plasma impedance, subsequent to an impedance matching unit in high frequency circuit, is varied complicatedly due to such causes as gas pressure, contamination of the chamber, CVD film deposition on the electrodes, etc. For this reason, up to date there is no power meter which can monitor the effective power accurately and instantly. Therefore, in the prior art method it is difficult to control the inter-electrode effective power, thus making the cleaning for each deposition cycle necessary.